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Discussion Starter #1
I have an 03 TJ with the I-6 motor. Noticed recently that system appeared to be losing coolant. I could find no visible leaks and so I took it to a local shop here for a pressure test. Mechanic says that he found a leak at the thermostat housing. He says he thinks he fixed it. I soon noticed the same coolant loss issue again. This time I got a UV additive and put it in the coolant. Upon checking with a black light, I could clearly see evidence of a leak from the bottom of the thermostat housing onto the top of the water pump. Having confirmed the leak I decided to replace the thermostat housing, gasket, thermostat and coolant sensor. On my first attempt to replace these items when I refilled the coolant it leaked from the housing like there was no gasket there at all. So I took it apart again and found that I had somehow cut the gasket which caused the leakage. After obtaining a new gasket (Fel-Pro) i installed the parts again but instead of refilling the whole system I just poured in enough coolant into the thermostat housing to fill it up to see if it would leak. There was no leak. So I refilled the coolant and ran the vehicle with the radiator cap off to check for thermostat functioning and to make sure no leaks appeared. The next morning I decided to drive the vehicle to work. I stopped at the Autozone to get another jug of coolant. When I came out I noticed a small puddle of green colored coolant underneath the radiator. I made a second stop and the same thing again. After work I went home and checked with the black light and again see evidence of a leak in the same area at the bottom of the thermostat housing. So it appears the leak is happening when the system is under pressure. I did not have a torque wrench when I installed the new housing so it may be possible that I did not apply sufficient torque. Any ideas would be appreciated. This is my first post to the forum. Thanks for any help.
 

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sounds like you just have to start over, make sure that all gasket surfaces are clean and smooth, use a quality gasket take youre time, torque wrench is not needed, snug up all the bolts so they feel the same. be sure that the housing isnt cracked. no need to apply 50 foot lbs to the bolts, just estimate 70 inch lbs or so. it may be the water pump gasket leaking.
 

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Discussion Starter #3
Thanks. All the things you mentioned with respect to surface prep were carefully done. My first action will be to torque the housing bolts to spec and see what that does for me. The water pump is not the leaking. It was replaced within the past year.
 

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With the thermostat being sideways, it can very easily slip out of it's groove while installing the housing
 

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Yup, Thermostat Housings can be tricky due to only 2 mounting bolts and tension from the upper radiator hose. Some 4L blocks can get by with just a gasket, others will need RTV on both sides of the gasket and RTV on the threads of the bolts.
 
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